Seborrhoeic keratoses appearing in sites of previous psoriasis plaques during treatment with efalizumab.

A 56-year-old man with recalcitrant psoriasis was treated with efalizumab, resulting in complete clearing of his skin lesions. However, multiple brown patches and papules, in the exact distribution of the previous psoriasis plaques, appeared on his lower legs. The pathological diagnosis was seborrhoeic keratoses (SKs) with overlapping features of solar lentigo. A variety of cutaneous adverse events has been observed in patients with psoriasis treated with efalizumab. To our knowledge, appearance of SKs after such treatment has not previously been reported. This may be due to the clinical insignificance of these benign skin tumours. However, it may be speculated whether efalizumab has an unknown effect in triggering the development of SKs in patients with psoriasis, and if this could shed any light on the pathogenesis of SKs.